A semiprecious gem is a type of gemstone that is not as valuable as a precious gem, such as a diamond. Jadestone, OPAL, and catseye are all examples of semiprecious gems. Jadestone is a type of green-colored stone that is often used in jewelry and carvings. OPAL is a type of gemstone that has a milky appearance and can come in a variety of colors. Catseye is a type of gemstone that has a unique banded pattern and is usually yellow or green in color.